Computer viruses can replicate themselves by making use of the knowledge that a specific piece of software code or data of application software or system software that always resides in the same relative location in memory for all instances of the software. This particular class of computer viruses often uses this knowledge to compromise a piece of software with known relative memory location in which the software resides in the memory. This is a problem faced by vendors and users of application and system software that do not employ virtual memory. Virtual memory is a method of allowing a computer appears to have more Random Access Memory (RAM) than it actually does. By utilizing available space on a hard disk, the operating system of the computer transparently swaps segments of memory contents between the hard disk and the RAM. Today, many software applications and system software codes are run on computer systems that do not employ the virtual memory method. This type of software is particularly vulnerable to attacks by the aforementioned class of viruses. This class of computer viruses seriously threatens many software applications and system codes that run on Personal Computer (PC), Personal Digital Assistant (PDA), mobile phones, and even switches and routers in the Internet.
Therefore, a need exists for a method for protecting computer systems that do not employ virtual memory against a class of computer viruses.